The trial of five men charged with gang-raping and murdering a young woman on a bus in New Delhi has opened with closed-door testimony from her friend who still bears the scars of injuries from the attack.

The 28-year-old software engineer, who may not be identified, is wheelchair-bound since the attack and is the prosecution's star witness in a case that has triggered nationwide protests, an intense debate about rampant crime against women in India and tougher anti-rape laws.

Although proceedings are subject to a gagging order, police allowed reporters to see the young man being taken in the company of lawyers and the judge to see the bus which has been parked in the court compound.

He then returned inside the courtroom where he was expected to be cross-examined by lawyers for the five adult accused, who have all denied murder, rape and robbery charges.

"My son will go to any lengths to ensure that the guilty are punished," the father had earlier told AFP as the two of them entered the courtroom in the Saket district.

"He will cooperate and is prepared to answer any questions posed by the defence."

Outrage over the crime prompted the government to hastily pass new legislation allowing for harsher penalties for sex crimes, including the death penalty.

The prosecution says it has large swathes of evidence, including DNA samples, the victim's blood-stained clothes, mobile phone records and eyewitness testimony.

The defence is expected to argue the evidence has been fabricated.

The trial is being held in front of one of India's recently created fast-track courts, aimed at dealing justice swiftly in a country where cases can often languish for years in the legal system.

Moscow's words and actions — including the alleged poisoning of a former spy — are not the results of random aggression but rather fall into distinct patterns that can help us anticipate Russia's next moves under Vladimir Putin.